I did not like too much of the first 6 episodes of the 5th season, but episodes 5.07 and 5.08 saved my belief on Lost and 5.09 was the best episode of the season - and one of the best ever.
The current setup is create: Island during the '77 and '97. Both sets full of interesting stuff & situations. This is Lost at its best - revealing the big picture while adding new intriguing elements on the picture. And Hugo asking "what if they start asking us questions we can't answer like who's president 1977?" from Sawyer - a classic. :D